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Working with interlaced footage

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Andres Bocan
Working with interlaced footage
on Jun 28, 2008 at 10:50:17 pm

Hi I am a bit new in doing special effects on Maya and I have some doubts.

I will work with 1080i 29,97 footage for some effects. Generally I will add 3D objects to some scenes.
I will track the camera in Boujou and I will export the data to Maya.

So when I create in Maya the image plane to have the reference of my background and adjust the track of the object, how will I see the fields of the footage ? I believe that I am just watching complete frames. If I add an interlaced footage to the image plane I just see one frame with both fields interlaced. With those ugly horizontal lines you know what I am talking about.

So how will I see individual fields to track my object properly ??

Thanks
Andres


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Alvaro Castaneda
Re: Working with interlaced footage
on Jun 29, 2008 at 6:50:07 am

what I usually do is I remove the fields in nuke or after effects, then export that as a image sequence, work on the in maya, tracking, compositing etc, and then at the end add fields back again an deliver to editorial, some time I don't have to add fields again cause they'll will add that for delivery.

good luk



----------------------
varomix - pixelEater
http://www.intelianimate.com


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Andres Bocan
Re: Working with interlaced footage
on Jun 29, 2008 at 10:30:24 pm

Alvaro:

OK it's easy if you have the chance of delivering it without fields but I have to finish the entire composition so I have to deliver the final shoot in the same format that I had recieved it. They will make the On Line with that.
So I have to deliver with fields.

If I will work without fields on Maya how will I composite it on After Effects to the original interlaced image ?

There must be an easy way to work with that. An interlaced footage is not an odd things that the most important 3D program does not take into account.!!!!!

Thanks
Andres


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Alvaro Castaneda
Re: Working with interlaced footage
on Jun 30, 2008 at 3:03:03 pm

hey

well, you can work everything with out fields in after effects, and add them in at render time, that's what I do, even in nuke, shake or whatever I'm doing my composition.

remove fields first, then composite, etc
and when finished just render WITH FIELDS, and you are done

hope that works for you

----------------------
varomix - pixelEater
http://www.intelianimate.com


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Andres Bocan
Re: Working with interlaced footage
on Jul 1, 2008 at 3:08:48 am

What I am not sure is..

When you deinterlace an image you lose Quality. In fact you have the half resolution of your entire image.
So when you interlace that, you don't recover that data.

My original footage where I will composite the 3D object is already interlaced. Taking this into account I am not sure how to work with that.

I need to animate the 3D Object in Maya following the movement field by field.



Thanks
Andres


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andrew strautz
Re: Working with interlaced footage
on Jun 29, 2008 at 10:13:04 am

I came a crossed this similar problem myself a while ago and I used what some might consider an odd solution though at the resolution it might take a while to set it up. when you create a plane give it height demensions of 1080 (or a custom resolution) and select every other polygon until you have your interlaced surface and apply a material to the selected faces. then select (useing the shortcut selection from the hypershade) the faces and invert the selection and apply another material to the others.

in the hypershade apply a shader map to the surface with a file texture leading to your image/video source selecting image sequance (make sure they are named correctly image.xxx.ext) and do the same to the second material.

they need to be unique and in no way currently connected.

now you need to select your second shader (the interlaced lines) and right click on the expression driven values of the image frames make sure the expression window is set to the expression object filter and select the expression for the second file texture, you can check for its name in the hierarchy of the material network, and apply the fallowing line.

file1.frameExtension=frame - 1; // (file1 is the name of the file node, frameExtension is the number of the frame to use and frame - 1 is the current frame minus one)

during playback the odd fields of the plane should be offset from the even by one frame. it can be adjusted easily by changing the " - 1" value of the script.

also for the night mare of setting this up (i'm sure, the most i ever did was a 640) you might want to reuse the basic scene file...

hope that helps.



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Andres Bocan
Re: Working with interlaced footage
on Jun 29, 2008 at 10:33:29 pm

Andrew:

I have to accept that I don't understand very well your explanation. You are right, it's really odd !! HAHAHAHA

There must be a way of working with interlaced footage in the most important 3D program, don't you
think ???
We are not talking about an odd format, just INTERLACED FOOTAGE.

Thanks
Andres


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andrew strautz
Re: Working with interlaced footage
on Jun 30, 2008 at 4:21:25 am

the jist of what i wrote is you are going to make a plane the height and width resolution of your source footage and give it enough segments for the height resolution so you can use the shaders to de-interlace the footage by applying the time offset material to the odd fields[polygons].

its a lot of work, espechily for such a simple scene but it will help you in the long run if you reuse it so you dont have to hop into an external program to de-interlace the footage (though i can guarantee it will be faster ^^; ) though since you asked how to do it in maya i gave the best answer i could ^^;



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Andres Bocan
Re: Working with interlaced footage
on Jul 1, 2008 at 3:03:57 am

OK but let me understand something.

Will you have each field in differents frames ?
I mean you need to animate the 3D object following the movement field by field.

How do you solve that in your workflow ? Sorry if I am not understanding very well the proccess.


Thanks
Andres


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andrew strautz
Re: Working with interlaced footage
on Jul 1, 2008 at 4:34:38 am

no no, you are useing one object with two materials on it, one material is for the even fields and one material is for the odd fields.

the polygon plane you are using is the height and width of your source footage and the height divisions are the same as your height resolution (this divides the UV space of the object into the resolution lines of the source footage). you select ever odd face of the polygon and apply the material for the odd fields then apply the even field material to the even faces.

after you apply the expression change to your scene it will deinterlace the footage since the odd fields are offset by one frame.

if you still don't understand i can make you a quick (much smaller) example.



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andres bocan
Re: Working with interlaced footage
on Jul 3, 2008 at 6:47:10 pm

Andrew:

OK I did what you have told me. OK it works, I can see the interlaced footage on the Image plane but...
I am not sure if I did it well, because what I really need is to have each fields in separate frames. What I mean is that I could work field by field. I should go through timeline field by field instead of going frame by frame.

I may see fields interlaced on image plane with your workflow, but they are together at the same frame in timeline, so in order to following field by field the live action to match, it does not work.

Do you understand what I mean ?

Thanks
Andres


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andrew strautz
Re: Working with interlaced footage
on Jul 4, 2008 at 12:05:59 am

well I'm not entirely sure what you say you need to accomplish but pretty much its pretty easy to adjust the offset, in the expression you either drop in a different number or you can assign it to an attribute you add to the plane to manipulate it faster.

pretty much this technique isn't for the rendering of the completed scene, its just a pass hack to render out the effects. after you have everything lined up correctly you should delete/hide the plane with the source footage and render the effect with interlacing to make it compatible when you composite it with the footage.

that's really the objective of that method.

i might be able to help you a little if i knew more about your project though.



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Alvaro Castaneda
Re: Working with interlaced footage
on Jul 4, 2008 at 12:13:05 am

I think you guys are making this harder than it is.

I done this a thousand time like I told you, this is NOT hard, don't over work this.

when I said "remove the fields" doesn't mean you only have 1, you make the image 1, out of the 2 fields.

just my humble opinion



----------------------
varomix - pixelEater
http://www.intelianimate.com


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Chad Briggs
Re: Working with interlaced footage
on Jul 5, 2008 at 2:16:00 pm

Guys, yeah, i think this is getting more complex than it might need to be. Fields can be overwhelming, but they are really pretty simple, you just have to get the "pattern" down.

The original post was "I will work with 1080i 29,97 footage for some effects". The real key here is to figure out the acqusition format, not the delivery format, as 1080i 29.97 can actually be a variety of diff formats (confusing i know, but bear with me) If your trying to match the footage exactly, the goal is to get the CG footage to match up with the "acquisition" footage exactly, meaning you need to work with whole frames. It's really easy to spot footage that has CG thats a diff frame rate than the original source footage or not interlaced the same, and really throws off the whole believability. But how to get whole frames, thats the rub.

Easiest way to tell import the footage into AFX, a frame sequencer, or just look at it in QT (if it's a QT file). Step through frame by frame. For the sake of discussion here W= whole frame, S= strobe frame/interlaced frame. As your stepping through, if you see it do something like WWWSS or SSWWW (or any kind of pattern like that), your footage was actually aquired at 23.976 fps, which means you can do a 3:2 pulldown in your comp program and get whole 24p footage. Then you just animate at 24fps, do your composite, then put the 3:2 pullup in at the last step in the process and now your back to 1080i 29.97

If your stepping through and there are NO strobe/interlace lines, the footage was probably acquired at 30p, so you just need to animate at 30p and your good to go.

If your stepping through and it's strobe/interlace lines on every frame, then it was shot at 60i. Best thing to do here is to take your footage and use a plugin to conver the footage to 60p. What happens is that it takes every frame, extracts the fields to two seperate frames (doubling the framerate) and guessing/interpolating on each frame what the missing information looks like. Then you animate your CG at 60fps, so it will line up with the processed footage. Then to get it back together you can do it two ways:
1.) work at 60fps in the comp all the way till the end. At the end, render out a 60fps sequence. Bring this back in to AFX (or wahtever) and put it in a 29.97 comp. When you render out of this, it will put the fields back in for you and it will all match up.
2.) from the get go, keep your comps at 29.97 and tell your footage that it's 60fps. Then when you render, it will look synced up.

There are some "gotchas" to watch out for. Namely in this case, if there is time remapping going on. If the footage has 3:2 pull up/down in it, and an editor has stretched the clip to make it longer or shorter, then your screwed :) The cadence of the pull up/down will be trashed. If you can get a unmolested peice of footage from the editor, thats the ideal situation, otherwise you'll just have to fudge it the best you can, by matching his time stretch, if you can find out what percentage he slowed it up/down.

This sounds complicated, but it's actually quite simple :) Hopefully this cleared stuff up, as we do this all the time and it's the #1 mistake i see younger compositors make, is not knowing how to work with fields. I really should probably do a tutorial on this at some point :)

cheers
Chad



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andres bocan
Re: Working with interlaced footage
on Jul 7, 2008 at 7:45:11 pm

Chad:

My original footage was shooted on film at 29,97. It was transfer to HD SR 1080i. 59,97 interlaced. And I receive the dpx Seq from that format.
So how do you consider I have to work ?


Andres


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Chad Briggs
Re: Working with interlaced footage
on Jul 12, 2008 at 2:22:31 pm

if the original footage was shot at 30p, and there is no visible interlacing, just work animate and composite at 29.97, and do not render to fields or interpet fields, and you should be fine.
Chad



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Andres Bocan
Re: Working with interlaced footage
on Jul 7, 2008 at 11:02:39 pm

Chad:

More simple than I explained you in teh previous message.
This is a TV project. So just think the original footage like 1080i 59,94 ftp (interlaced footage)


Andres


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